1. Field of the Invention
The present invention relates to a speaker including a substantially semi-spherical piezoelectric ceramic member and more particularly to a speaker which is constructed for use, for example, as a super-tweeter used in reproducing DVD audio or super-audio CDs.
2. Description of the Related Art
A piezoelectric ceramic speaker which is related to the speaker described and claimed herein is disclosed in U.S. patent application Ser. No. 08/760,639 which is the parent application of the present Continuation-In-Part Application. The speaker described in U.S. patent application Ser. No. 08/760,639 has a vibrating section made of a semi-spherical piezoelectric body and is constructed by connecting the vibrating section and a base section which sections are separately formed of different materials. The vibrating section is mounted on the base section with insulation materials located therebetween.
Because this related speaker is constructed by using an adhesive to connect the vibrating section and the base section which are separately formed of different materials, the manufacturing efficiency and the acoustic characteristics of the sound output thereby are not uniform or of high quality as is desired. Furthermore, a high harmonic mode of the semi-spherical piezoelectric body is generated as spurious in about half of a fundamental resonance frequency by profile vibration of the semi-spherical end surface. In addition, although the base section is required to have insulation material for accommodating connecting terminals, the base section often requires an increased thickness because the specific weight of the base section usually made of synthetic resin is too light which causes a draw or concave recess during molding of the base section.
To overcome the problems described above, the preferred embodiments of the present invention provide a speaker which is adapted and constructed to allow increased efficiency of manufacturing and substantially uniform and excellent acoustic characteristics of sound output thereby.
According to one preferred embodiment of the present invention, a speaker includes a semi-spherical vibrating section, driving electrodes for vibrating the vibrating section, and a base section for holding the vibrating section, wherein the vibrating section and the base section comprise a unitary, integral molded piezoelectric body.
When electrical signals are input to the driving electrodes, the vibrating section vibrates due to a piezoelectric effect and emits sound waves from the curved semi-spherical surfaces of the vibrating body in the inventive speaker according to the preferred embodiments of the present invention. Because of the semi-spherical shape of the vibrating body, sound waves are transmitted omnidirectionally and are not limited to only certain directional sound wave transmission as is common in prior art speakers.
Because the vibrating section and the base section are molded as a single unitary body of piezoelectric material, a step and material required for bonding the vibrating section and the base section to each other required in related speakers is eliminated. Thus, the number of parts and manufacturing and assembly steps are reduced and ease and efficiency of fabrication is increased. Further, with the novel structure of the preferred embodiments of the present invention, profile vibration in the high order mode is suppressed because of the unitary construction of the vibrating section and the base section, thereby improving the acoustic characteristics of the speaker.
It is preferable that the vibrating section and the base section are molded and formed such that a ratio of weight relative to each other is about 1:5 to about 1:20 for the purpose of improving the acoustic characteristics of the speaker. More specifically, the inventor of the present application determined that acoustic characteristics of the inventive speaker are greatly improved when an outline vibration mode of the semi-spherical surfaces of the vibrating body is suppressed as much as possible. The inventor also determined that the outer edges of the curved semi-spherical surfaces of the vibrating body should be fixed to suppress the outline vibration mode of the vibrating body. However, the inventor discovered that when the outer edges of the curved semi-spherical surfaces of the speaker body are fixed to a support member such as a speaker box, for example, and the base section of the speaker vibrates, the acoustic characteristics of the speaker are changed. This problem of changing speaker acoustic characteristics is solved and uniform high quality acoustic characteristics are achieved by molding the vibrating section and the base section such that a ratio of weight relative to each other is about 1:5 to about 1:20.
In addition, it is preferable to dispose the driving electrodes on a surface of the vibrating section and to have a portion of the driving electrodes extend onto the base section. As a result of this arrangement of the driving electrodes, it is easier to connect the electrodes with external circuits by extending the driving electrodes located on the surface of the vibrating section onto the base section.
It is also preferable to form mounting notches or holes in the base section to allow the speaker to be attached to a support member such as a case or box.